Magnetic discs have typically been fabricated on conductive metal substrates. During formation of some or all of the multiple layers of the magnetic medium on the conductive substrate, a bias voltage is applied to the substrate while it is positioned in a processing chamber. Biasing the substrate causes ions within the processing chamber to be accelerated toward the substrate. Depending upon the particular process used, the acceleration of ions toward the substrate surface increases the material deposition rate on the substrate in comparison with an unbiased substrate, modifies the substrate surface by ion bombardment, or produces other desirable effects.
In the case of a conductive substrate, the bias voltage may be applied to the substrate through conductive fingers that physically hold the substrate in position for processing. For example, FIG. 1 shows a three-finger substrate holder 100 that supports a substrate 102. The substrate holder 100 includes a holder body 104 and three conductive support rods 106, 108 and 110 that extend from the holder body 104 to make contact with the edge of the substrate 102. Although not specifically shown in FIG. 1, the support rods 106, 108 and 110 typically terminate in a V-shape or forked-shape to provide stability for the substrate 102 during transport and processing.
It is becoming increasingly desirable to use non-conductive substrates in some applications. For example, glass substrates are utilized in the fabrication of magnetic discs for laptop computers because of their light weight and durability. However, a problem arises in the processing of non-conductive substrates because the substrate cannot be biased by application of a voltage in the same way as in the processing of conductive substrates. As mentioned above, in the processing of conductive substrates, the bias voltage can be applied to the substrate though the support rods of the substrate holder. However, this has not proven practical in the case of non-conductive substrates due to the fact that the V-shaped or fork-shaped support rods of the substrate holder that hold the non-conductive substrate erect for processing shadow the area of the substrate adjacent to the support rods. This shadowing prevents a conductive layer from building up adjacent to the rods and, thus, prevents the formation of a conductive path between the support rods and the conductive film being formed on the non-conductive substrate. Thus, the same electrical path used in the case of conductive substrates (conductive support rods to disc) cannot be used with non-conductive substrates. In the case of non-conductive substrates, this problem may be overcome by rotating the substrate during processing to make sure that the support rods do not shadow the formation of conductive layers adjacent the rods. However, substrate rotating mechanisms generally occupy one process station on a sputter tool having a limited number of processing stations, thereby decreasing the processing efficiency of the tool, and ultimately resulting in higher processing costs per disc.
Accordingly, there is a need for improved apparatus and methods for processing non-conductive substrates so that the non-conductive substrate can be electrically biased to enhance substrate processing steps.